Air conditioning and television as protective factors in arboviral encephalitis risk

In California, the advent of television and air conditioned housing has coincided with a general decrease in mosquito-borne viral encephalitis cases in humans in the past 25 years. During this same period, levels of vector populations, virus activity in vectors, birds, and horses has been high at times. Air conditioning and television encourage persons to remain indoors during summer evenings, the primary time when infected Culex tarsalis transmit western equine encephalomyelitis and St. Louis encephalitis viruses. The attack rates for these 2 diseases in 33 counties in the central valley of California, 1945-1982, were compared with the prevalence of household air conditioning and television. Encephalitis rates were negatively associated with television ownership in both cross-sectional and longitudinal analysis. Moreover, individual counties which experienced the most rapid increase in household television ownership had the greatest decline in encephalitis rates. A telephone survey conducted in Kern County revealed that air conditioner and television utilization times corresponded closely to the feeding times of Cx. tarsalis, and respondents indicated a preference to remain indoors during this time because of these appliances. It is concluded that changed behavioral patterns may protect from vector-borne diseases and be complementary to vector control programs.